1. Field of the Invention
This invention relates to an engine speed control device for a watercraft engine, and in particular to a throttle valve opening control device that controls engine operation to be more sensitive to acceleration when operating in a propulsion condition and less sensitive to acceleration when operating in a trolling condition.
2. Description of the Related Art
In general, with regard to watercrafts, a user who wants to enjoy fishing is apt to run a watercraft in a high speed operation toward a fishing ground and also to move in a trolling operation (low speed operation) in the fishing ground. Particularly, adjusting a speed for setting bait adrift is one of the most important factors to get a target fish in the trolling operation. Thus, fine speed adjustment is desired at a low speed. When the watercraft transfers to the propulsion condition from the trolling condition, improvement of responsiveness in the watercraft operation is desired so that the watercraft rapidly changes to the high speed condition from the low speed condition.
In conventional watercraft engines, an operator control is used to accelerate the watercraft engine. The movement of the operator control mechanically moves a throttle valve via a cam, such that the throttle valve is adjusted in a non-linear manner relative to the movement of the operator control. However, the mechanical structure in conventional engine speed control devices makes it difficult to provide reduced sensitivity to acceleration when operating the watercraft in a trolling condition, while also providing increased responsiveness to acceleration when operating the watercraft in a propelling condition.
In contrast, electrically operated throttling devices that provide for variable throttle valve operation based on the position of an accelerator control are available in four-wheeled vehicles. One such device is disclosed, for example, in Japanese Patent Application No. JP 2004-036574.
However, known technology for throttling devices in four-wheeled vehicles does not adequately provide the engine speed control desired in watercraft operation. For example, in watercraft, a trolling operation is desirable, where the engine speed sometimes operates at or below an idle speed of the engine. It is difficult to use a four-wheeled throttling technology to provide reduced sensitivity to acceleration in a watercraft when operating in the trolling condition, while also providing increased sensitivity or responsiveness to acceleration when operating in a propulsion condition. Accordingly, there is a need for an improved engine speed control device for watercraft.